Lithium-manganese composite oxide granular secondary particle, method for production thereof and use thereof

ABSTRACT

Granular secondary particles of a lithium-manganese composite oxide suitable for use in non-aqueous electrolyte secondary batteries showing high-output characteristics which are granular secondary particles made up of aggregated crystalline primary particles of a lithium-manganese composite oxide and have many micrometer-size open voids therein with a defined average diameter and total volume of open voids. A process for producing the granular secondary particles which includes spray-drying a slurry of at least a manganese oxide, a lithium source, and an agent for open-void formation to thereby granulate the slurry and then calcining the granules.

TECHNICAL FIELD

The present invention relates to a lithium-manganese composite oxidepowder, a process for producing the same, and a non-aqueous electrolytesecondary battery as a use of the powder.

BACKGROUND ART

For use as a positive active material for non-aqueous electrolytesecondary batteries, a lithium-manganese composite oxide is used in theform of a powder composed of granular secondary particles of anappropriate size formed by the sintering of crystalline primaryparticles. Several processes have hitherto been used as processes forproducing granular secondary particles. For example, JP-A-2000-169151discloses a process comprising obtaining a lithium-manganese compositeoxide by the reaction of electrolytic manganese dioxide with lithiumcarbonate, wherein the size of the electrolytic manganese dioxide as astarting material is regulated by pulverization to thereby enable thegranular secondary particles to retain this size even after thereaction. JP-A-10-172567 discloses a process in which a slurry preparedby dispersing a powder of electrolytic manganese dioxide in an aqueoussolution of a water-soluble lithium compound is spray-dried andgranulated to obtain granular secondary particles. Furthermore,JP-A-10-228515 and JP-A-10-297924 disclose a process in which a finepowder is compacted/aggregated with a roller compactor or the like toobtain granular secondary particles.

As can be seen from those documents, priority has hitherto been given todensifying granular secondary particles as much as possible to heightenpowder packing density from the standpoint of heightening the dischargecapacity of batteries per unit volume. Consequently, there have been alimited number of documents which disclose granular secondary particlescharacterized by the structure thereof, in particular, by the voidspresent therein.

Among the documents which disclose granular secondary particlescharacterized by the voids present therein is, for example,JP-A-2002-75365. This technique is intended to provide a positive activematerial excellent in high-rate charge/discharge characteristics andcycle characteristics by forming voids within the particles of apositive active material. However, these voids are closed voids and notconnected to the environment surrounding the particles. Because of this,the diffusion of lithium ions into the liquid electrolyte isinsufficient and the improvements in high-rate characteristics and cyclecharacteristics have been insufficient. Specifically, although high-ratecharge/discharge characteristics are evaluated in that patent documentin terms of ratio between the capacity in current flowing at 2.0C. andthe capacity in current flowing at 0.2C. in the page 5, Table 2 therein,the values of this capacity ratio are 90% or lower, indicating that thehigh-rate charge/discharge characteristics are insufficient.

DISCLOSURE OF THE INVENTION

The invention has been achieved after directing attention to thestructural regulation of granular secondary particles of alithium-manganese composite oxide, in particular, the state of openvoids in the granular secondary particles.

An object of the invention is to provide a lithium-manganese compositeoxide positive active material suitable for use as a constituentmaterial for a non-aqueous electrolyte secondary battery having highoutput characteristics and a process for producing the active material.

Another object of the invention is to provide a non-aqueous electrolytesecondary battery employing the lithium-manganese composite oxidepositive active material having excellent properties.

The invention provides the lithium-manganese composite oxide, processfor producing the same, and non-aqueous electrolyte secondary batterydescribed below. The objects of the invention are accomplished withthese.

(1) Granular secondary particles of a lithium-manganese composite oxidewhich are granular secondary particles made up of aggregated crystallineprimary particles of a lithium-manganese composite oxide, characterizedin that

the granular secondary particles have many micrometer-size open voidstherein, the open voids having an average diameter in the range of from0.5 to 3 μm and the total volume of the open voids being in the range offrom 3 to 20 vol. % on average based on the total volume of the granularsecondary particles.

(2) The granular secondary particles of a lithium-manganese compositeoxide as described in (1) above, characterized in that the granularsecondary particles have a specific surface area of from 0.2 to 1.0 m²/gand an average diameter of from 5 to 30 μm, and the crystalline primaryparticles constituting the granular secondary particles have an averagediameter of from 0.5 to 4.0 μm.

(3) The granular secondary particles of a lithium-manganese compositeoxide as described in (1) above, characterized by being represented bythe compositional formula Li_(X)M_(Y)Mn_(3-X-Y)O_(4-Z)F_(z) (wherein X,Y, and Z are such numbers that X=1.0 to 1.2, Y=0 to 0.3, and Z=0 to 0.3;and M represents one or more elements selected from Al, Co, Ni, Cr, Fe,and Mg).

(4) The granular secondary particles of a lithium-manganese compositeoxide as described in (1) above, characterized in that the content ofone or more boric acid compounds contained as an impurity in thegranular secondary particles of a lithium-manganese composite oxide islower than 0.0005 in terms of molar ratio between the manganese andboron (B/Mn) contained in the lithium-manganese composite oxide.

(5) The granular secondary particles of a lithium-manganese compositeoxide as described in (4) above, characterized in that the boric acidcompounds contained as an impurity are lithium borate and/or lithiumsodium borate.

(6) A process for producing the granular secondary particles of alithium-manganese composite oxide as described in (1) above,characterized by comprising spray-drying a slurry prepared by dispersinga fine powder of a manganese oxide and a fine powder of lithiumcarbonate or by dispersing a fine powder of a manganese oxide, a finepowder of lithium carbonate, and a compound containing one or moreelements selected from Al, Co, Ni, Cr, Fe, and Mg to thereby granulatethe slurry and then calcining the granules at a temperature of from 700to 900° C.

(7) The process for producing granular secondary particles of alithium-manganese composite oxide as described in (6) above,characterized in that the fine powder of a manganese oxide and the finepowder of lithium carbonate have an average particle diameter of 1 μm orsmaller.

(8) A process for producing the granular secondary particles of alithium-manganese composite oxide as described in (1) above,characterized by comprising spray-drying a slurry prepared by dispersinga fine powder of a manganese oxide, a lithium source, and an agent foropen-void formation or by dispersing a fine powder of a manganese oxide,a fine powder of lithium carbonate, a compound containing one or moreelements selected from Al, Co, Ni, Cr, Fe, and Mg and an agent foropen-void formation to thereby granulate the slurry and then calciningthe granules at a temperature of from 700 to 900° C.

(9) The process for producing granular secondary particles of alithium-manganese composite oxide as described in (8) above,characterized in that the agent for open-void formation is a substancewhich has an average particle diameter of 1 μm or smaller and disappearsupon heating.

(10) The process for producing granular secondary particles of alithium-manganese composite oxide as described in (6) above,characterized in that a compound which is a compound of an element otherthan manganese, lithium, fluorine, v and aluminum, cobalt, nickel,chromium, iron, and magnesium is not an agent for open-void formation isadded as an additive to the slurry.

(11) The process for producing granular secondary particles of alithium-manganese composite oxide as described in (10) above,characterized in that the additive is a boron compound, and that thecompound is added to the slurry in an amount in the range of from 0.0005to 0.05 in terms of molar ratio between manganese and boron (B/Mn) and,after the calcining, the boron is removed by water washing to such adegree that the molar ratio (B/Mn) decreases to below 0.0005.

(12) A non-aqueous electrolyte secondary battery characterized byemploying the granular secondary particles of a lithium-manganesecomposite oxide as described in (1) above as a positive active material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of a section of granular secondary particles asthe sample in Example 2.

FIG. 2 is a photograph of a section of granular secondary particles asthe sample in Comparative Example 2.

FIG. 3 is a photograph of a section of granular secondary particles asthe sample in Comparative Example 6.

FIG. 4 is a graphic presentation showing the discharge ratecharacteristics of the samples in Example 2, Comparative Example 2, andComparative Example 6.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention has been achieved based on the finding that the size andamount of open voids present in granular secondary particles of alithium-manganese composite oxide are factors which govern the dischargerate characteristics (the property corresponding to the high-ratecharge/discharge characteristics in JP-A-2002-75365) of non-aqueouselectrolyte secondary batteries employing this oxide as a positiveactive material. Namely, the granular secondary particles of alithium-manganese composite oxide of the invention are characterized inthat many micrometer-size open voids are present in network arrangementin the particles, and that the size of these voids is in the range offrom 0.5 to 3 μm in terms of average diameter and the amount thereof isin the range of from 3 to 20 vol. % on average based on the volume ofthe granules.

The most characteristic feature resides in that many micrometer-sizeopen voids are present in network arrangement in the granular secondaryparticles (hereinafter often referred to simply as “granules”). As aresult, the discharge rate characteristics of batteries can be improved.

The micrometer-size open voids are specified by size and amount. Thesize thereof is from 0.5 to 3 μm in terms of average diameter, and theamount thereof is from 3 to 20 vol. % on average based on the granulevolume. In case where the average particle diameter of the open voids issmaller than 0.5 μm, the battery has reduced discharge ratecharacteristics. In case where the open voids have a size exceeding 3μm, the strength of the granules is difficult to maintain. The mostpreferred range of the average diameter is from 1.0 to 2.5 μm.

In case where the proportion of the open voids is lower than 3 vol. %,the battery has reduced discharge rate characteristics. In case wherethe proportion thereof exceeds 20 vol. %, it is difficult to secure ahigh powder packing density required of electrode materials. The mostpreferred range of the proportion of the open voids is from 5 to 15 vol.%.

Incidentally, the average diameter and amount of the open voids arevalues determined through the approximation of the open voids tospheres. The values thereof can be determined by a method whichcomprises taking a scanning electron photomicrograph of a section ofgranules and subjecting the photograph to image analysis; these valuesare number-average values obtained by averaging the found values for atleast 500 voids.

Besides having many open voids, the granular secondary particles of theinvention are preferably further characterized in that the granules havea specific surface area of from 0.2 to 1.0 m²/g and an average diameterof from 5 to 30 μm and that the crystalline primary particlesconstituting the granules have an average diameter of from 0.5 to 4.0μm. These values are preferred in order for the granules to bring aboutthe maximum secondary-battery performances when used as a positiveactive material. For example, specific surface areas thereof exceeding1.0 m²/g or diameters of the crystalline primary particles smaller than0.5 μm are undesirable because use of such granules results inconsiderable deterioration of charge/discharge capacity with cycling ata temperature of 50° C. or higher. Specific surface areas thereofsmaller than 0.2 m²m/g or diameters of the crystalline primary particlesexceeding 4.0 μm are undesirable because use of such granules result ina decrease in discharge rate characteristics. Average diameters of thegranular secondary particles outside the range of from 5 to 30 μm areundesirable from the standpoint of constituting a sheet electrode.

The lithium-manganese composite oxide of the invention is preferablyrepresented by the compositional formulaLi_(X)M_(Y)Mn_(3-X-Y)O_(4-Z)F_(z) (wherein X, Y, and Z are such numbersthat X=1.0 to 1.2, Y=0 to 0.3, and Z=0 to 0.3; and M represents one ormore elements selected from Al, Co, Ni, Cr, Fe, and Mg). The values ofX, which indicates lithium content, and Y, which indicates the contentof the element M, are important in determining charge/discharge capacityand stability to charge/discharge cycling. Especially preferred rangesof X and Y are such that X=1.05 to 1.15, Y=0.05 to 0.25, and X+Y=1.15 to1.30.

When boric acid compounds are present on the surface of the granules andwithin the open voids in a certain amount or larger, adverse influencesare exerted on battery performances. The preferred range of boric acidcompound amount in which the compounds exert no influence on batteryperformances is such that the molar ratio of boron to manganese (B/Mn)is lower than 0.0005. This ratio is more preferably lower than 0.0003.

The process of the invention for producing the granular secondaryparticles is characterized by comprising spray-drying a slurry preparedby dispersing a fine powder of a manganese oxide and a fine powder oflithium carbonate to thereby granulate the slurry and then calcining thegranules at a temperature of from 700 to 900° C., or by comprisingspray-drying a slurry prepared by dispersing a fine powder of amanganese oxide, a lithium source, and an agent for open-void formationto thereby granulate the slurry and then calcining the granules at atemperature of from 700 to 900° C.

Examples of the manganese oxide powder include electrolytic manganesedioxide, chemically synthesized manganese dioxide, Mn₃O₄, Mn₂O₃, and thelike.

Examples of the lithium source include lithium hydroxide and lithiumnitrate, which are water-soluble, and lithium carbonate, which isinsoluble in water. In the case where lithium carbonate, which isinsoluble in water, is used as a lithium source, the particle sizes ofthe lithium carbonate and the manganese oxide are an important factorwhich governs the size of voids because this lithium carbonate servesalso as an agent for open-void formation. The particle size thereof isdesirably on the submicrometer order, and is preferably 1 μm or smaller,more preferably in the range of from 0.3 to 0.7 μm, in terms of theaverage particle diameter of the powdery mixture of the lithiumcarbonate and the manganese oxide. Such a particle size is easilyattained by adding a powder of a manganese oxide and a powder of lithiumcarbonate to water and mixing the ingredients with pulverization. Asapparatus for the pulverization/mixing can be used a ball mill,oscillating mill, mill of the wet medium stirring type, and the like.

Incidentally, in the case where open voids having a larger total volumeare desired, an agent for open-void formation other than lithiumcarbonate may be added.

A water-soluble lithium source such as lithium hydroxide or lithiumnitrate can be used as a lithium source besides lithium carbonate.

In this case, it is necessary to use an agent for open-void formationand the particle size of this agent for open-void formation is animportant factor which governs the size of voids. The particle sizethereof is desirably on the submicrometer order. Specifically, it ispreferably 1 μm or smaller, more preferably in the range of from 0.3 to0.7 μm. Such a particle size of the agent for open-void formation iseasily attained by adding a powder of a manganese oxide, a lithiumsource, and a powder of the agent for open-void formation to water andsubjecting these ingredients to wet pulverization/mixing. As apparatusfor the pulverization/mixing can be used a ball mill, oscillating mill,mill of the wet medium stirring type, and the like.

As the agent for open-void formation is used a substance whichdisappears upon heating, such as, e.g., carbon black, carbon nanotubes,or graphite.

The amount of voids can be regulated by changing the amount of the agentfor open-void formation and the amount of lithium carbonate. The amountof voids is preferably from 3 to 20 vol. %, most preferably from 5 to 15vol. %, on average based on the volume of the granules.

The slurry which has undergone the wet pulverization/mixing isgranulated by spray drying. The spray drying can be conducted with anordinary spray dryer in which a slurry is sprayed with a rotating diskor fluid nozzle and drying the droplets with hot air. Granulationtechniques other than spray drying can be used, such as, e.g., thein-liquid granulation method and rolling granulation method. However,spray drying is most advantageous industrially.

A compound of an element other than manganese and lithium, e.g., acompound of aluminum, chromium, or the like, is often added for thepurpose of heightening the performance of the lithium-manganesecomposite oxide of the invention as a positive active material. In thecase where a compound of the element M is added, it is preferred to addit in the form of an oxide of the element or a precursor (hydroxide,etc.) for the oxide. With respect to methods for the addition thereof,it is desirable to add it to the slurry comprising a manganese oxide andlithium carbonate before the wet pulverization/mixing.

The addition of a boron compound as described in (11) above is conductedfor the purpose of regulating the shape of the crystalline primaryparticles of the lithium-manganese composite oxide. This attains theformation of open voids in even network arrangement. As the boroncompound can be used H₃BO₃, B₂O₃, Li₂O.nB₂O₃ (n=1 to 5), or the like.The compound is added before calcining, and is desirably added to theslurry before spray drying. The amount of the compound to be added ispreferably in the range of from 0.0005 to 0.05, more preferably in therange of from 0.01 to 0.001, in terms of molar ratio to manganese(B/Mn). After calcining, the boron compound remains as a boric acidcompound on the surface of the composite oxide granules and in the openvoids. Since the remaining boron compound exerts adverse influences onbattery performances, it is preferred to remove it by water washing tosuch a degree that the molar ratio of boron to manganese (B/Mn)decreases to below 0.0005.

The preferred range of boric acid compound amount in which the compoundexerts no influence on battery performances is such that the molar ratioof boron to manganese (B/Mn) is lower than 0.0005. This ratio is morepreferably lower than 0.0003.

The non-aqueous electrolyte secondary battery employing thelithium-manganese composite oxide of the invention as a positive activematerial shows excellent discharge rate characteristics. The excellentdischarge rate characteristics are presumed to have been brought aboutby the many open voids present in even network arrangement in thegranular secondary particles of a lithium-manganese composite oxide ofthe invention. Namely, the following is presumed. Discharge rateimproves as lithium ion transport within the positive active materialbecomes easier. As a result of the formation of the network structure ofthe positive active material due to the many open voids, the distanceover which lithium ions are transported between the positive activematerial and the liquid electrolyte surrounding the same has decreasedand, hence, the transport has become easy.

EXAMPLES

The invention will be explained below in detail by reference toExamples, but the invention should not be construed as being limited tothe following Examples.

Example 1

A lithium carbonate powder (average particle diameter, 7 μm), a powderof electrolytic manganese dioxide (average particle diameter, 3 μm), andboric acid were used in such weighed amounts as to result in thecomposition Li_(1.1)Mn_(1.9)B_(0.01)O₄. Water was added thereto in anappropriate amount. Thereafter, the particulate ingredients werepulverized with a mill of the wet medium stirring type for 1 hour. Waterwas added thereto in such an amount as to give a slurry having a solidconcentration of 15 wt %. The water was vaporized with a spray dryer toobtain spherical granular dry particles. The spray drying was conductedat a hot-air inlet temperature of 250° C. This dry powder was calcinedat 850° C. for 5 hours to obtain a lithium-manganese composite oxide.Furthermore, this oxide was washed in 95° C. hot water bath for 1 hour,recovered by filtration, and then dried to obtain a sample.

Examples 2 to 4

Samples were obtained in completely the same manner as in Example 1,except that each of aluminum hydroxide, chromium oxide, and nickelhydroxide powders was used as an additive (M) besides the lithiumcarbonate, electrolytic manganese dioxide, and boric acid powders inExample 1 and these ingredients were mixed in such weighed amounts as toresult in the composition Li_(1.1)M_(0.1)Mn_(1.8)B_(0.01)O₄ (M=Al, Cr,or Ni).

Example 5

A sample was obtained in completely the same manner as in Example 1,except that a lithium fluoride powder and an aluminum hydroxide powderwere used as additives besides the lithium carbonate, electrolyticmanganese dioxide, and boric acid powders in Example 1 and theseingredients were mixed in such weighed amounts as to result in thecomposition Li_(1.03)Al_(0.16)Mn_(1.81)B_(0.005)O_(3.8)F_(0.2).

Example 6

A sample was obtained in completely the same manner as in Example 1,except that an aluminum hydroxide powder was used as an additive besidesthe lithium carbonate, electrolytic manganese dioxide, and boric acidpowders in Example 1 and these ingredients were mixed in such weighedamounts as to result in the compositionLi_(1.08)Al_(0.15)Mn_(1.78)B_(0.01)O₄.

Example 7

A sample was obtained in completely the same manner as in Example 1,except that an aluminum hydroxide powder was used as an additive besidesthe lithium carbonate, electrolytic manganese dioxide, and boric acidpowders in Example 1 and these ingredients were mixed in such weighedamounts as to result in the compositionLi_(1.01)Al_(0.33)Mn_(1.67)B_(0.01)O₄.

Example 8

A sample was obtained in completely the same manner as in Example 1,except that an aluminum hydroxide powder was used as an additive besidesthe lithium carbonate, electrolytic manganese dioxide, and boric acidpowders in Example 1 and these ingredients were mixed in such weighedamounts as to result in the compositionLi_(1.12)Al_(0.01)Mn_(1.88)B_(0.01)O₄.

Example 9

A sample was obtained in completely the same manner as in Example 1,except that an aluminum hydroxide powder was used as an additive besidesthe lithium carbonate, electrolytic manganese dioxide, and boric acidpowders in Example 1 and these ingredients were mixed in such weighedamounts as to result in the compositionLi_(1.2)Al_(0.1)Mn_(1.8)B_(0.01)O₄.

Example 10

A sample was obtained in completely the same manner as in Example 1,except that an aluminum hydroxide powder was used as an additive besidesthe lithium carbonate, electrolytic manganese dioxide, and boric acidpowders in Example 1 and these ingredients were mixed in such weighedamounts as to result in the compositionLi_(1.1)Al_(0.1)Mn_(1.8)B_(0.005)O₄.

Example 11

A lithium carbonate powder (average particle diameter, 7 μm), a powderof electrolytic manganese dioxide (average particle diameter, 3 μm), andboric acid were used in such weighed amounts as to result in thecomposition Li_(1.1)Mn_(1.9)B_(0.01)O₄. These ingredients weretransferred to a pot made of nylon and containing balls made ofzirconia. After water was added thereto in an appropriate amount, theparticulate ingredients were pulverized with a ball mill for 48 hours.Water was further added to the resultant slurry to regulate the solidconcentration therein to 15 wt %. This slurry suffered no solid/liquidseparation even through 2-hour standing, showing that it had asatisfactory dispersion state. The water was vaporized from the slurrywith a spray dryer to obtain spherical dry particles. The spray dryingwas conducted at a hot-air inlet temperature of 250° C. and an outlettemperature of 140° C. The powder obtained was calcined at 850° C. for10 hours to obtain a sample. This sample was dissolved in hydrochloricacid and this solution was examined with an ICP to conduct compositionalanalysis. The composition of the sample including boric acid compoundswas Li_(1.1)Mn_(1.9)B_(0.01)O₄. The atomic ratio between the manganesein the lithium-manganese composite oxide and the boron in the boric acidcompounds, B/Mn, was 0.0053.

Example 12

Completely the same procedure as in Example 11 was conducted, exceptthat aluminum hydroxide was added to the lithium carbonate powder,electrolytic manganese dioxide powder, and boric acid powder in Example11 and these ingredients were mixed in such weighed amounts as to resultin the composition Li_(1.1)Al_(0.1)Mn_(1.8)B_(0.01)O₄. The compositionof the sample obtained including boric acid compounds wasLi_(1.1)Mn_(1.8)Al_(0.1)B_(0.01)O₄. The molar ratio between themanganese in the lithium-manganese composite oxide and the boron in theboric acid compounds (B/Mn) was 0.0056.

Example 13

Completely the same procedure as in Example 11 was conducted, exceptthat chromium oxide Cr₂O₃ was added to the lithium carbonate powder,electrolytic manganese dioxide powder, and boric acid powder in Example11 and these ingredients were mixed in such weighed amounts as to resultin the composition Li_(1.1)Cr_(0.1)Mn_(1.8)B_(0.01)O₄. The compositionof the sample obtained including boric acid compounds wasLi_(1.1)Mn_(1.8)Cr_(0.1)B_(0.01)O₄. The molar ratio between themanganese in the lithium-manganese composite oxide and the boron in theboric acid compounds (B/Mn) was 0.0056.

Example 14

Completely the same procedure as in Example 11 was conducted, exceptthat aluminum hydroxide and lithium fluoride were added to the lithiumcarbonate powder, electrolytic manganese dioxide powder, and boric acidpowder in Example 11 and these ingredients were mixed in such weighedamounts as to result in the compositionLi_(1.1)Al_(0.1)Mn_(1.8)B_(0.01)O_(3.9)F_(0.1). The composition of thesample obtained including boric acid compounds wasLi_(1.1)Al_(0.1)Mn_(1.8)B_(0.01)O_(3.9)F_(0.1). The molar ratio betweenthe manganese in the lithium-manganese composite oxide and the boron inthe boric acid compounds (B/Mn) was 0.0056.

Example 15

The spinel lithium manganate powder obtained in Example 12 was suspendedin water in a slurry concentration of 20 wt %. This suspension wasstirred at 95° C. for 6 hr. Thereafter, the solid matter was recoveredby filtration and dried to obtain a sample. The sample obtained wasdissolved in hydrochloric acid and this solution was examined with anICP to conduct compositional analysis. The composition of the sampleincluding boric acid compounds was Li_(1.1)Mn_(1.8)Al_(0.1)B_(0.0004).The molar ratio between the manganese in the lithium-manganese compositeoxide and the boron in the boric acid compounds (B/Mn) was 0.00022.

Comparative Example 1

A sample was obtained in completely the same manner as in Example 1,except that the lithium carbonate powder was replaced with a lithiumhydroxide monohydrate (LiOH.H₂O) powder. Incidentally, the lithiumhydroxide monohydrate in the slurry before spray drying was in the stateof being completely dissolved in the water.

Comparative Examples 2 to 4

Samples were obtained in completely the same manners as in Examples 2 to4, except that the lithium carbonate powder was replaced with a lithiumhydroxide monohydrate (LiOH.H₂O) powder. Incidentally, the lithiumhydroxide monohydrate in the slurry before spray drying was in the stateof being completely dissolved in the water.

Comparative Example 5

A sample was obtained in completely the same manner as in Example 5,except that the lithium carbonate powder was replaced with a lithiumhydroxide monohydrate (LiOH.H₂O) powder. Incidentally, the lithiumhydroxide monohydrate in the slurry before spray drying was in the stateof being completely dissolved in the water.

Comparative Example 6

A powder of electrolytic manganese dioxide (average particle diameter,15 μm) and a powder of lithium carbonate (average particle diameter, 3μm) were dry-blended with each other in such weighed amounts as toresult in the composition Li_(1.12)Mn_(1.88)O₄. Thereafter, the mixturewas calcined at 900° C. for 12 hours to obtain a sample in which thestarting materials had been converted to a lithium-manganese compositeoxide.

Example 16

The mixed particles of manganese dioxide and lithium carbonate containedin the slurry which was subjected to spray drying in Example 1 wereexamined for particle size with a laser diffraction/scattering particlesize analyzer. As a result, the volume-average particle diameter thereofwas 0.65 μm, and the standard deviation indicating the width of particlesize distribution was 0.07.

Example 17

The samples of Examples 1 to 10, Comparative Examples 1 to 5, andComparative Example 6 were examined for composition by chemicalanalysis, for specific surface area with a BET measuring apparatus, forthe average diameter of the granular secondary particles with a laserdiffraction/scattering particle size analyzer, and for the averagediameter of the crystalline primary particles constituting the granuleswith a scanning electron microscope. The results shown in Table 1 wereobtained.

TABLE 1 Composition of Average diameter Average diameter granularsecondary Boron Specific of granular of crystalline particles of amountsurface area secondary primary particles composite oxide B/Mn (m²/g)particles (μm) (μm) Example 1 Li_(1.08)Mn_(1.92)O₄ 0.0001 0.55 19.7 1.5Example 2 Li_(1.08)Al_(0.10)Mn_(1.82)O₄ 0.0002 0.44 18.5 1.8 Example 3Li_(1.07)Cr_(0.09)Mn_(1.84)O₄ 0.0001 0.56 19.5 1.2 Example 4Li_(1.07)Ni_(0.10)Mn_(1.83)O₄ 0.0001 0.50 21.0 1.2 Example 5Li_(1.02)Al_(0.15)Mn_(1.83)O_(3.8)F_(0.2) 0.0002 0.38 17.5 2.0 Example 6Li_(1.07)Al_(0.15)Mn_(1.78)O₄ 0.0002 0.51 19.1 1.7 Example 7Li_(1.00)Al_(0.33)Mn_(1.67)O₄ 0.0001 0.52 17.9 1.6 Example 8Li_(1.11)Al_(0.01)Mn_(1.88)O₄ 0.0001 0.50 18.5 1.5 Example 9Li_(1.10)Al_(0.10)Mn_(1.80)O₄ 0.0002 0.48 16.8 1.6 Example 10Li_(1.09)Al_(0.10)Mn_(1.81)O₄ 0.0002 0.49 19.7 1.7 ComparativeLi_(1.07)Mn_(1.93)O₄ 0.0001 0.48 18.5 1.4 Example 1 ComparativeLi_(1.08)Al_(0.09)Mn_(1.83)O₄ 0.0002 0.40 19.0 1.8 Example 2 ComparativeLi_(1.07)Cr_(0.10)Mn_(1.83)O₄ 0.0002 0.48 20.3 1.5 Example 3 ComparativeLi_(1.07)Ni_(0.10)Mn_(1.83)O₄ 0.0001 0.42 18.0 1.0 Example 4 ComparativeLi_(1.02)Al_(0.16)Mn_(1.82)O_(3.8)F_(0.2) 0.0002 0.40 15.5 1.7 Example 5Comparative Li_(1.11)Mn_(1.89)O₄ 0.0001 0.40 13.8 1.6 Example 6

Example 18

With respect to the samples of Examples 1 to 10, Comparative Examples 1to 5, and Comparative Example 6, photographs of sections of granularsecondary particles were taken with a scanning electron microscope.Samples for this photographing were prepared by embedding a powder in acurable resin and polishing a surface thereof to expose sections ofgranules. The electron photomicrographs were subjected to image analysisto determine the average diameter and amount of open voids present inthe granular secondary particles. The results shown in Table 2 wereobtained. Examples of the electron photomicrographs of granule sections(Example 2, Comparative Example 2, and Comparative Example 6) are shownin FIGS. 1 to 3. The values of average open-void diameter werenumber-average values for from 500 to 1,000 voids.

TABLE 2 Composition of Average granular secondary open-void Amount ofparticles of diameter open voids composite oxide (μm) (vol %) Example 1Li_(1.08)Mn_(1.92)O₄ 1.8 9.1 Example 2 Li_(1.08)Al_(0.10)Mn_(1.82)O₄ 2.28.4 Example 3 Li_(1.07)Cr_(0.09)Mn_(1.84)O₄ 2.8 12.2 Example 4Li_(1.07)Ni_(0.10)Mn_(1.83)O₄ 2.5 5.5 Example 5Li_(1.02)Al_(0.15)Mn_(1.83)O_(3.8)F_(0.2) 1.5 15.5 Example 6Li_(1.07)Al_(0.15)Mn_(1.78)O₄ 2.4 8.2 Example 7Li_(1.00)Al_(0.33)Mn_(1.67)O₄ 2.1 8.3 Example 8Li_(1.11)Al_(0.01)Mn_(1.88)O₄ 2.3 8.5 Example 9Li_(1.10)Al_(0.10)Mn_(1.80)O₄ 2.2 8.5 Example 10Li_(1.09)Al_(0.10)Mn_(1.81)O₄ 2.0 8.1 Comparative Li_(1.07)Mn_(1.93)O₄1.1 2.0 Example 1 Comparative Li_(1.08)Al_(0.09)Mn_(1.83)O₄ 0.9 2.5Example 2 Comparative Li_(1.07)Cr_(0.10)Mn_(1.83)O₄ 0.7 1.5 Example 3Comparative Li_(1.07)Ni_(0.10)Mn_(1.83)O₄ 1.5 2.0 Example 4 ComparativeLi_(1.02)Al_(0.16)Mn_(1.82)O_(3.8)F_(0.2) 0.8 1.8 Example 5 ComparativeLi_(1.11)Mn_(1.89)O₄ 0.3 0.5 Example 6

Example 19

The slurries obtained in Examples 11 to 14 were added in a small amountto methanol and dispersed therein with ultrasonic. The particle diameterdistribution was determined by the laser diffraction/scattering method.The results concerning the volume-average particle diameter of theparticles constituting each slurry are shown in Table 3. The standarddeviation indicating the width of particle size distribution was about0.5 for each slurry. Subsequently, with respect to the samples obtainedin Examples 11 to 15, a 10-g portion was placed in a measuring cylinderand the volume thereof was measured before and after 50 vibrations todetermine the bulk density of the powder. The average particle diameterwas determined by the measuring method described above. The results arealso shown in Table 3. Furthermore, the structures of the samplesobtained in Examples 11 to 15 were examined with a scanning electronmicroscope. As a result, the crystalline primary particles in eachsample had a size of from 1 to 5 μm and an average particle diameter ofabout 2 μm. The granular secondary particles had an average diameter ofabout 20 μm and were spherical.

TABLE 3 Volume- Volume- average average particle Bulk density ofparticle diameter of lithium diameter particles manganate powder oflithium constituting (g/cm³) manganate slurry Before After powder (μm)vibrations vibrations (μm) Example 11 0.7 1.1 1.7 18 Example 12 0.5 1.21.7 20 Example 13 0.6 1.1 1.6 19 Example 14 0.7 1.3 1.8 20 Example 15 —1.2 1.7 20

Example 20

The samples obtained in Examples 11 and 12 were mixed with a conductivematerial/binder (acetylene black/Teflon) to obtain positive-electrodematerials. Using lithium metal as a negative-electrode material andusing an ethylene carbonate/dimethyl carbonate solution of LiPF₆ as aliquid electrolyte, coin batteries were fabricated. A charge/dischargetest was conducted at 60° C. and a current density of 0.4 mA/cm² in avoltage range of from 4.3 to 3.0 V. The retention in cycling wasdetermined from a difference in discharge capacity between the 10thcycle and the 50th cycle. The results shown in Table 4 were obtained.

TABLE 4 Composition determined by analysis (Composition oflithium-manganese Initial composite oxide discharge Retention includingboric acid capacity in cycling compound) (mAh/g) (%/cycle) Example 11Li_(1.1)Mn_(1.9)B_(0.01)O₄ 104 99.94 Example 12Li_(1.1)Al_(0.1)Mn_(1.8)B_(0.01)O₄ 95 99.97 Example 13Li_(1.1)Cr_(0.1)Mn_(1.8)B_(0.01)O₄ 96 99.96 Example 14Li_(1.1)Al_(0.1)Mn_(1.8)B_(0.01)O_(3.9)F_(0.1) 100 99.97 Example 15Li_(1.1)Al_(0.1)Mn_(1.8)B_(0.0004)O₄ 96 99.98

Example 21

With respect to the samples of Examples 1 to 10, Comparative Examples 1to 5, and Comparative Example 6, discharge rate characteristics wereexamined. Each sample powder was mixed with a conductive material/binder(acetylene black/Teflon resin) to obtain a positive-electrode material.Using lithium metal as a negative-electrode material and using anethylene carbonate/dimethyl carbonate solution of LiPF₆ as a liquidelectrolyte, coin batteries were fabricated. These batteries wereexamined for discharge rate at room temperature. Examples of the resultsof the measurement are shown in FIG. 4. Furthermore, the rate retention(proportion of discharge capacity at 5.5 C. to discharge capacity at 0.3C.) and discharge capacity for each sample are shown in Table 5. It isapparent that the samples of Examples 1 to 10 are superior in dischargerate characteristics to the samples of Comparative Examples 1 to 5 andComparative Example 6.

TABLE 5 Composition of granular secondary Rate Discharge particles ofretention capacity composite oxide (%) (mAh/g) Example 1Li_(1.08)Mn_(1.92)O₄ 99.0 110 Example 2 Li_(1.08)Al_(0.10)Mn_(1.82)O₄99.3 102 Example 3 Li_(1.07)Cr_(0.09)Mn_(1.84)O₄ 99.0 100 Example 4Li_(1.07)Ni_(0.10)Mn_(1.83)O₄ 99.1 95 Example 5Li_(1.02)Al_(0.15)Mn_(1.83)O_(3.8)F_(0.2) 98.8 105 Example 6Li_(1.07)Al_(0.15)Mn_(1.78)O₄ 99.0 100 Example 7Li_(1.00)Al_(0.33)Mn_(1.67)O₄ 99.1 105 Example 8Li_(1.11)Al_(0.01)Mn_(1.88)O₄ 98.9 102 Example 9Li_(1.10)Al_(0.10)Mn_(1.80)O₄ 99.1 101 Example 10Li_(1.09)Al_(0.10)Mn_(1.81)O₄ 99.2 103 Comparative Li_(1.07)Mn_(1.93)O₄92.0 111 Example 1 Comparative Li_(1.08)Al_(0.09)Mn_(1.83)O₄ 91.5 104Example 2 Comparative Li_(1.07)Cr_(0.10)Mn_(1.83)O₄ 91.0 100 Example 3Comparative Li_(1.07)Ni_(0.10)Mn_(1.83)O₄ 91.5 93 Example 4 ComparativeLi_(1.02)Al_(0.16)Mn_(1.82)O_(3.8)F_(0.2) 92.0 104 Example 5 ComparativeLi_(1.11)Mn_(1.89)O₄ 92.5 103 Example 6

INDUSTRIAL APPLICABILITY

The granular secondary particles of a lithium-manganese composite oxideof the invention show excellent discharge rate characteristics when usedas the positive active material of a non-aqueous electrolyte secondarybattery. The granular particles are hence useful especially as apositive active material for high-output lithium ion secondarybatteries. Heightening the output of lithium ion secondary batteries isdesired especially in application to hybrid electric cars, and thegranular particles can be an effective material therefor. The granularparticles can be utilized as a useful positive active material also inother applications of lithium ion secondary batteries, such as, e.g.,power sources for purely electric cars, power storage, and portableappliances. The granular particles of the invention are highly worthy ofindustrial use.

1. Granular secondary particles of a lithium-manganese composite oxidewhich are granular secondary particles made up of aggregated crystallineprimary particles of a lithium-manganese composite oxide, characterizedin that the granular secondary particles have many micrometer-size openvoids therein, the open voids having an average diameter in the range offrom 0.5 to 3 μm and the total volume of the open voids being in therange of from 3 to 20 vol. % on average based on the total volume of thegranular secondary particles.
 2. The granular secondary particles of alithium-manganese composite oxide of claim 1, characterized in that thegranular secondary particles have a specific surface area of from 0.2 to1.0 m²/g and an average diameter of from 5 to 30 μm, and the crystallineprimary particles constituting the granular secondary particles have anaverage diameter of from 0.5 to 4.0 μm.
 3. The granular secondaryparticles of a lithium-manganese composite oxide of claim 1, which arerepresented by the compositional formulaLi_(X)M_(Y)Mn_(3−x−y)O_(4−Z)F_(Z) (wherein X, Y, and Z are such numbersthat X=1.0 to 1.2, Y=0 to 0.3, and Z=0 to 0.3; and M represents one ormore elements selected from Al, Co, Ni, Cr, Fe, and Mg).
 4. The granularsecondary particles of a lithium-manganese composite oxide of claim 1,characterized in that the content of one or more boric acid compoundscontained as an impurity in the granular secondary particles of alithium-manganese composite oxide is lower than 0.0005 in terms of molarratio between the manganese and boron (B/Mn) contained in thelithium-manganese composite oxide.
 5. The granular secondary particlesof a lithium-manganese composite oxide of claim 4, characterized in thatthe boric acid compounds contained as an impurity are lithium borateand/or lithium sodium borate.
 6. A process for producing the granularsecondary particles of a lithium-manganese composite oxide of claim 1,characterized by the process comprising pulverizing a slurry comprisingmanganese oxide and lithium carbonate to produce a slurry comprisingmanganese oxide particles having an average particle diameter of 1micrometer or smaller and lithium carbonate particles having an averageparticle diameter of 1 micrometer or smaller or pulverizing a slurrycomprising manganese oxide, lithium carbonate and a compound containingone or more elements selected from Al, Co, Ni, Cr, Fe, and Mg to producea slurry comprising manganese oxide particles having an average particlediameter of 1 micrometer or smaller, lithium carbonate particles havingan average particle diameter of 1 micrometer or smaller, and a compoundcontaining one or more elements selected from Al, Co, Ni, Cr, Fe, andMg, spray drying the slurry to thereby granulate the slurry and thencalcining the granules at a temperature of from 700 to 900° C.
 7. Theprocess for producing granular secondary particles of alithium-manganese composite oxide of claim 6, characterized in that acompound which is a compound of an element other than manganese,lithium, fluorine, aluminum, cobalt, nickel, chromium, iron, andmagnesium and is not an agent for open-void formation is added as anadditive to the slurry.
 8. The process for producing granular secondaryparticles of a lithium-manganese composite oxide of claim 7,characterized in that the additive is a boron compound, and that thecompound is added to the slurry in an amount in the range of from 0.0005to 0.05 in terms of molar ratio between manganese and boron (B/Mn) and,after the calcining, the boron is removed by water washing to such adegree that the molar ratio (B/Mn) decreases to below 0.0005.
 9. Aprocess for producing the granular secondary particles of alithium-manganese composite oxide of claim 1, characterized bycomprising spray-drying a slurry prepared by dispersing a fine powder ofa manganese oxide, a lithium source, and an agent for open-voidformation or by dispersing a fine powder of a manganese oxide, a finepowder of lithium carbonate, a compound containing one or more elementsselected from Al, Co, Ni, Cr, Fe, and Mg, and an agent for open-voidformation to thereby granulate the slurry and then calcining thegranules at a temperature of from 700 to 900° C.
 10. The process forproducing granular secondary particles of a lithium-manganese compositeoxide of claim 9, characterized in that the agent for open-voidformation is a substance which has an average particle diameter of 1 μmor smaller and disappears upon heating.
 11. A non-aqueous electrolytesecondary battery characterized by employing the granular secondaryparticles of a lithium-manganese composite oxide of claim 1 as apositive active material.